2007 AMC 8 第 4 题
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所有题目均经美国数学协会（MAA）官方合法授权使用。
4.
一座鬼屋有六扇窗。幽灵 Georgie 从一扇窗进入，并从另一扇不同的窗离开，共有多少种方式？
A haunted house has six windows. In how many ways can Georgie the Ghost enter the house by one window and leave by a different window?
答案：D
小提示：
先选择进入的窗户
Choose the entrance window first.
大提示：
进入窗户确定后，离开的窗户少一个选择
After the entrance is chosen, the exit has one fewer option.
解答：
Georgie 有 种选择进入的窗户。但离开时只能选择不同的窗户，所以有 种选择。
路径总数为 。
所以正确答案是 D。
Georgie has options for which window he enters through. He, however, only has options for the exit since it must be different from the entrance.
The total number of paths is therefore
Thus, D is the correct answer.
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